Containers are well known in which a metal, releasable cap closure Traditionally, the cap is screw fitted onto the body such that the upper surface of the neck of the container seals against the layer of sealing compound. Filling speeds for such containers are generally up to about 500 containers per minute.
Because of the time taken to fit a screw closure during production, a modified arrangement has been developed in which a closure is formed with sealing compound moulded to the outer part of the closure end wall and to the inside of the closure sidewall or skirt. This kind of closure may be push fitted onto a screw threaded container during production of a filled container. Filling speeds for such containers may be up to about 1,000 containers per minute. The screw threads of the body dig into the sealing compound to form at least a partial thread therein such that, when the container comes to be opened, relative rotation of the closure and container body will break the seal and allow the closure to be removed. This arrangement is useful for certain food products where a partial vacuum is maintained in the container after filling and closure. During the filling process of the container, steam is injected into the open container in the head space above the hot food product which has been measured into the container. The closure is then pressed down onto the container and, as the steam condenses, a partial vacuum is formed in the container above the head space which acts to hold the closure firmly in place on the container body. In the fully cooled filled container, the typical vacuum in the container is about 0.3 bar. This partial vacuum must be vented to allow the cap closure to be removed.
In another known container, a glass container body in the form of a glass tumbler is formed with an annular bead around its upper end. The tumbler body is molded and then treated to melt its upper end edge to form the bead which is smooth for drinking. A flexible aluminium closure is snapped over the bead and forms a seal with the body by virtue of a partial vacuum formed in container during processing. The seal is broken by prying off the closure.
A steel closure cannot be used in this arrangement since steel is not sufficiently flexible for use in a pry-off closure.